​Ta có: \(4 H \left(\right. x \left.\right) = \left(\right. 2 x \left.\right)^{2} - 2.2 x . y + y^{2} + 3 y^{2} - 4 x + 4 y + 4\)

\(= \left(\right. 2 x - y \left.\right)^{2} - 2 \left(\right. 2 x - y \left.\right) + 3 y^{2} + 2 y + 3 + 1\)

\(= \left(\right. 2 x - y - 1 \left.\right) + 3 \left(\right. y^{2} + \frac{2}{3} y + 1 \left.\right)\)

\(= \left(\right. 2 x - y - 1 \left.\right) + 3 \left(\left(\right. y + \frac{1}{2} \left.\right)\right)^{2} + \frac{8}{3} \geq \frac{8}{3}\).

Vậy giá trị nhỏ nhất của \(E\) là: \(\frac{8}{3} : \&\text{nbsp}; 4 = \frac{2}{3}\) tại \(x = \frac{2}{3} ; \&\text{nbsp}; y = - \frac{1}{3}\)